It is the principal objective of the proposed research to elucidate the metabolism and function of phospholipids, essential building blocks of biological membranes throughout nature. The biosynthesis of sphingomyelin and its relation to the synthesis of phosphatidylcholine will be studied in animal cells in culture. The mechanism of the rapid transbilayer movement of phospholipids in membanes of B. megaterium will also be investigated. Another major aspect of the proposed program is the regulation of the synthesis of membrane lipids in animal tissues and in bacteria.